BOSTON, Aug 22 (Reuters) - Massachusetts Secretary of State William Galvin, one of the most aggressive U.S. securities law enforcers, next month will face his first primary challenge in over a decade from a rival who claims Galvin has neglected his role as the state’s top election overseer.

Boston City Councilor Josh Zakim, Galvin’s 34-year-old challenger in the Sept. 4 primary, won the backing of Democratic state convention delegates in June and the endorsement of Boston Mayor Marty Walsh, who supports his voter rights focus.

Zakim argues that Galvin during his 24 years in office has been slow to back election reforms, including same-day voter registration. Seventeen other states allow that practice.

“People want to make sure their voices are heard,” Zakim said in an interview outside Boston City Hall on Wednesday. “They’re entitled to have their voices heard.”

Galvin, 67, in March defended in court a state requirement that people register to vote 20 days before an election, and the rule was deemed constitutional in a July decision.

Galvin, who last faced a competitive primary in 2006, says he personally supports same-day registration but was defending a rule put in place by state legislators.

Galvin said he was not surprised that his elections role is attracting more attention given Democrats’ increased national focus on voting after Republican President Donald Trump’s 2016 election.

While securities regulation has largely not come up during the campaign, Galvin called it the “principal job of the office.”

His cases over the years have targeted Putnam Investments, Goldman Sachs and Scottrade Inc. In June, he charged MetLife Inc with making false statements to investors related to failing to pay pension benefits to retirees.

“I’m not frustrated. I continue to talk about other aspects of the office, but I’m also quite happy to talk about elections as we have a great record,” Galvin said in a Friday phone interview.

At the end of July, Galvin’s campaign reported $2.8 million in cash on hand, compared to $585,230 for the Zakim campaign, disclosures with the state show.

Zakim said despite his elections focus, protecting investors would be a priority if he unseated Galvin. He expressed interest in cryptocurrencies and said he wanted to provide clear guidance on how they would be regulated.

But Zakim said he believed his voting rights message has resonated among Democrats.

“People want to see folks who share their values as secretaries of state defending the democracy,” he said. (Reporting by Nate Raymond in Boston; Editing by Scott Malone and Cynthia Osterman)